1. Field of Invention
The present invention corresponds to Magnetic Resonance Imaging (MRI) and more specifically to modular receive coils for MRI.
2. Discussion of Prior Art
Typically surface coils may be used in Magnetic Resonance (MR) Imaging to receive MR response signals for a region of a subject to create an MR image of that region.
Best results occur when the region imaged is at a depth from the surface coil being approximately the diameter of the surface coil. This provides a high signal/noise (S/N) ratio image. A disadvantage is that the field-of-view (FOV) tends to be small.
Several surface receive coils may be used, termed "phased array coils" to provide a larger FOV. Phased array coils are described in U.S. Pat. No. 4,825,162 Roemer, Edelstein "Nuclear Magnetic Resonance (NMR) Imaging with Multiple Surface Coils" issued Apr. 25, 1989, assigned to the present assignee and hereby incorporated by reference. Phased array coils must have predefined overlap between them in order to reduce coil "coupling" which reduces the S/N ratio, and are generally pre-constructed on a fixed surface. Since the degree of flux through each coil changes as the coils are distorted, they are also typically constructed on a non-flexible material.
The S/N ratio drops off as coils move away from the intended imaging volume, and the surface coils must be as close as possible to the surface of the subject. The use of phased array coils on rigid boards does not allow the coils to conform to the surface of the subject, resulting in a low S/N ratio image.
Also, different receive coils are used to image different parts of a subject. Head coils are typically used to image a subject's head and a body coil or flat surface coil typically are used to image a subject's back.
U.S. Pat. No. 5,435,302 "Flexible Surface Coils for Use in Nuclear Magnetic Resonance Imaging" by Lenkinski et al. issued Jul. 25, 1995 describes the use of a single flexible MR surface receive coil which conforms to the surface of the subject's face or neck. This, however, does not describe how to make coils to image different parts of a subject's anatomy, and also requires a special coil for imaging the neck as opposed to one used for imaging orbits of a subject's eyes.
Currently, there is a need for MR surface receive coils which have a large field of view, fit closely to surface of subject, have a large signal-to-noise ratio, and may be used to easily image different parts of subject.